High blood pressure, including essential hypertension, is a major risk factor of stroke, congestive heart failure, coronary heart disease and other cardiovascular diseases. The identification and study of childhood precursors of hypertension which could lead to methods effective in the prevention of adult hypertension is a major goal of the National High Blood Pressure in the Young Program, Epidemiology Branch, DHVD, NHLBI, of which this study is a part. Considerable evidence suggests that heredity plays a large and important role in determining blood pressure, particularly as it relates to essential hypertension. In the proposed study the mode of inheritance of genes involved with blood pressure regulation and associated variables will be investigated with an aim to providing information relevant to the epidemiology of hypertension. Particular attention will be paid to a search for major genes by using recently developed statistical methods designed for segregation and linkage analysis of quantitative traits in large pedigrees. Five large (75-350 members) families have been ascertained, each through a proband with essential hypertension; four of these families are White and one is Black. Most members participated in an extensive data collection protocol involving variables of an anthropometric, biochemical, genetic, medical, physiological, psychological and sociological nature. Among the measured variables are: subcutaneous fat thicknesses; plasma lipid, lipoprotein and renin levels; urinary kallikrein and aldosterone levels; genetic markers (blood types, etc.); physical examination and clinical laboratory findings: systolic time intervals in response to numerous stresses; personality assessments; and socioeconomic status. The identification of genetic effects including major gene influences in variables related to essential hypertension may help define important epidemiologic factors that: 1) relate to increased risk of hypertension; 2) account for differences in blood pressure among various subgroups of the population; 3) can identify children that have high risk for developing hypertension; 4) can identify homogeneous groups for further study of disease etiology.